1. Field of the Invention
The present invention concerns a crossed polarization directional antenna system intended in particular for cellular telephones.
2. Description of the Prior Art
Document U.S. Pat. No. 5,710,569 describes a directional antenna system including a flat reflector and an array of antennas carried by the reflector. Each antenna is a dipole defined by two straight conductor members mounted on two supports for fixing them to the reflector and is connected to the + and - terminals of a power supply. The antennas of the array are aligned with one axis of the reflector. They are of single polarization within the array.
Document U.S. Pat. No. 5,030,962 describes a crossed polarization directional antenna structure including a substrate of high electrical resistivity, in particular of silicon, an array of antennas formed on the substrate and a dielectric lens associated with the system. Each antenna comprises two dipoles and four diodes interconnecting the dipoles in pairs. The diodes are connected in a loop and therefore connect the four branches of the two dipoles, two opposite diodes in the loop being of opposite polarity to the other two.
In the above antenna structure the passive components defined by the dipoles and the active components such as the diodes and possible other components associated with the dipoles are fabricated by multilayer photo-etching on the substrate.
In particular, the branches of the dipoles are each in the form of a straight and narrow conductive strip or a triangular conductive plate and are opposed in pairs, the respective axes of the two dipoles being orthogonal.
These double polarization antennas of the prior art are designed for radar applications and operate at very high frequencies, in the order of 100 GHz. They are not suitable for mobile telephone applications, for which antennas must be particularly robust mechanically and transmit in a wide band around a predefined frequency less than the frequencies of the previously cited prior art structure, for example around 915 MHz for GSM transmission, 1,780 MHz for DCS transmission or 1,920 MHz for PCS transmission.
The aim of the present invention is to provide a compact crossed polarization directional antenna system suitable for mobile telephones.